The organic EL device is a charge injection type self emitting device utilizing the light emission generated at the time of recombining an electron and a positive hole reaching at a light emitting layer. Such an organic EL device has been developed actively since 1987 when T. W. Tang, et al. proved that an device comprising laminated thin films of a fluorescent metal chelate complex and a diamine based molecule emits a light of a high luminance with a low driving voltage.
The device configuration of the organic EL device basically comprises cathode/organic layer/anode. The organic layer thereof in general has a two layer structure comprising a light emitting layer and a positive hole injection layer, or a three layer structure comprising an electron transporting layer, a light emitting layer and a positive hole transporting layer. In the organic EL device, it is necessary to supply charges (a positive hole and an electron) to a light emitting material to be the luminescent center efficiently and quickly. For that purpose, a charge transporting material is contained in the light emitting layer, or a positive hole transporting layer is disposed between the anode and the light emitting layer, or an electron transporting layer is disposed between the cathode and the light emitting layer.
Such a light emitting layer and the charge (positive hole, electron) transporting layer, the charge injecting layer and so on, which are formed adjacent to the light emitting layer as occasion demands, are typically formed by a vacuum deposition method. In a vapor deposition method such as the vacuum deposition or the like, however, there are problems that a large scale deposition apparatus is required and a cost thereof is expensive. Furthermore, there is another problem of difficulty in application for a large surface area of a substrate. In order to solve these problems, there is proposed an organic EL device in which the light emitting layer or the charge transporting layer is formed by a wet film forming method (a spin coating method, a printing method, an ink jet method, etc.) in which an organic compound having a light emitting property, a charge transporting property or the like is dissolved or dispersed in a solvent and applied onto a substrate. The wet film forming method using a solvent for an application to a substrate has merits including the following facts that a large scale deposition apparatus is not required, a production process can be simplified, a material can be utilized efficiently, a cost is low, and the process can be applied to a large surface area of a substrate, in comparison with the vacuum deposition method.
On the other hand, a dendrimer is a new type polymer having a highly branched structure, which is proposed by Tomalia et al. on 1984. Owing to its structure in which many branches extend from a “core” which is a center of the molecule, it is also called a dendritic polymer. It is understood that, since branched-chains extend outside of the core in the form of layers (these layers are called “generations”), the density of the branches is higher toward the outside, so that the structure can capture a metal ion or the like inside of the dendrimer as a molecule capsule, or an electron or energy migration from the outside into the core can be induced.
As an example of an application of the dendrimer to the organic EL device, there is disclosed a method of applying a solution mixture of a low molecular host and a low molecular phosphorescent guest arranged at a center of a conjugated dendrimer (e.g. S.-C. Lo et al., Adv. Mater., (2002), vol. 14, No. 13-14, p. 975-979). Furthermore, there is also disclosed a method of using a multi-functioned dendrimer in which a low molecular phosphorescent guest is arranged at a center of the dendrimer and at least a part of branches (dendrons) has a host material (e.g. Japanese Patent Application Laid-Open No. 2003-231692). Furthermore, in a document, “Nature”, (2002), Vol. 415, p. 509-511, there is disclosed a phenyl azomethine dendrimer comprising an azomethine structure having a high coordinating property to metal ions, and in a document titled “Kanagawa Academy of Science and Technology (KAST) Summary of Studies in 2001”, KAST, 2002, p 101-116, there is disclosed an organic EL device using a phenyl azomethine dendrimer.